Synthetic polyester multifilament yarns have been known and used commercially for several decades, having been first suggested by W. H. Carothers, U.S. Pat. No. 2,071,251, and then by Whinfield and Dickson, U.S. Pat. No. 2,465,319. Most of the polyester polymer that has been manufactured and used commercially for such continuous filament yarns has been poly(ethylene terephthalate), sometimes referred to as 2G-T. This polymer is often referred to as homopolymer, although it is known that, in addition to the residues of ethylene, from ethylene glycol, and terephthalate residues, from dimethyl terephthalate or terephthalic acid, there are also residues from diethylene glycol. For textile (apparel) purposes, such commercial homopolymer is usually of intrinsic viscosity about 0.6; it can vary up to about 0.65 or even 0.67, and can also be of somewhat lower viscosity. Commercial homopolymer is notoriously difficult to dye. Such homopolymer is mostly dyed with disperse dyestuffs at high temperatures under elevated pressures, which is a relatively expensive and inconvenient process (in contrast to processes for dyeing several other commercial fibers at atmospheric pressure, e.g. at the boil), and so there have been several suggestions for improving the dyeability of polyester yarns.
Accordingly, Griffing and Remington, U.S. Pat. No. 3,018,272, suggested the use of cationic-dyeable copolyesters, in which the poly(ethylene terephthalate) structure is modified by inclusion of sulfonate groups that provide an affinity for cationic dyestuffs. Such cationic-dyeable copolyester consisting essentially of poly[ethylene terephthalate/ 5-(sodium sulfo) isophthalate] containing about 2 mole % of the 5-(sodium sulfo) isophthalate groups in the polymer chain has been used commercially as a basis for polyester yarns for some 20 years, and is sometimes referred to as 2G-T/SSI. Although this cationic-dyeable copolyester is significantly more expensive than the homopolymer, which is not cationic dyeable, and has also provided weaker fibers than does homopolymer, cationic-dyeable copolyester has been used on a large scale for various applications, especially as staple fiber, for spun yarns, because, in addition to the useful and improved dyeing capability of the copolyester, the individual fibers break more readily than 2G-T fibers, and this tendency to break is of great advantage in spun yarns, in providing improved pilling performance. In contrast, the lower strength has generally been a disadvantage of the cationic dyeable copolyester in filament yarns.
2G-T/SSI has also been used in heather multi-filament yarns, wherein cationic-dyeable copolyester filaments are intermingled with homopolymer filaments, that are not cationic dyeable. Heather yarns were disclosed by Reese in U.S. Pat. No. 3,593,513, and Lee in U.S. Pat. No. 4,059,949. Heather yarns were preferably made by cospinning the filaments so as to mix the filaments during their spinning.
The present invention is not concerned with heather yarns, i.e. yarns that contain significant amounts of differently-dyeable filaments, This invention is concerned only with a need to make useful textured yarns that consist essentially entirely of filaments that have cationic-dyeable characteristics.
A large amount of homopolymer has been used to make draw-textured polyester yarns from draw-texturing feed yarns (DTFY) that are substantially amorphous spin-oriented multi-filament (continuous filament) yarns prepared by spinning at withdrawal speeds of the order of about 3000 ypm or more. This concept was first suggested by Petrille in U.S. Pat. No. 3,771,307 and Piazza and Reese in U.S. Pat. No. 3,772,872.
As indicated, conventional homopolymer DTFY has been manufactured in large quantities and has been draw-textured. Hitherto, however, although 2G-T/SSI copolymer has been used satisfactorily for many years to make other types of polyester yarns as indicated, customers have complained about DTFY from 2G-T/SSI and about the results of texturing DTFY made from 2G-T/SSI copolyester. Despite many efforts over the years hitherto, it has not proved possible to improve 2G-T/SSI copolyester DTFY to meet customer requirements in this regard at an economic price.
It is an object of the invention to provide a cationic-dyeable copolyester DFTY that meets such requirements. In other words, the problem has been to provide DTFY that consists essentially of filaments having cationic-dyeability, but that does not give rise to the defects complained of heretofore.
Cemel et al., U.S. Pat. No. 4,233,363, disclosed heather DTFY. In other words, Cemel required a mixed filament DTFY, that must have two different types of spin-oriented filaments, one type being of a cationically-dyeable copolymer and the other being differently dyeable, namely homopolymer. Most of Cemel's disclosure is about the need for intimate mixing (measured as high DFI) and closely matching elongations of the two different components (so as to get the desired heather). All Cemel's working Examples cospin conventional (monocomponent) filaments of the two types of differently dyeable filaments. In column 10, lines 54-57, Cemel adds that, if desired, some of the filaments may be of a sheath-core structure, as disclosed, e.g. in Lee, referred to above. As indicated already, the present invention is not concerned with heather yarns.
Reference is also made to EP A2 0285437, which discloses an improved cationic-dyeable DTFY of concentric sheath/core bicomponent filaments, with a sheath of 2G-T/SSI copolyester and a core of 2G-T homopolymer. Further reference will be made to this hereinafter, as an object of the invention is to provide a further improvement, beyond that disclosed specifically in the Examples of EP A2 0285437.